enable /sys/class/power_supply/battery/energy_now in android kernels

[Andy Doan]

The battery (at least for nexus7) provides a pretty decent software interface to gather energy usage metrics. However, the stock kernels don't have this enabled.

The patches already exist for the nexus7:

 patch 1: https://android-review.googlesource.com/#/c/50742/
 patch 2: https://android-review.googlesource.com/#/c/50732/

I've tested these in my local build without issues.

I don't have access to the other devices we support, so I'm not sure what work is needed for those.

[Andy Doan (doanac)]

I think getting this enabled for nexus7 now would be sufficient for our needs

[Andy Doan (doanac)]

According to Leann:

The Raring image I believe had issues
with a patch we were carrying to enable the Touchscreen in the desktop
image, but broke the touchscreen in the phablet image so we all agreed
to wait to use the Ubuntu Nexus 7 Kernel until Saucy. So I'm going to
assume this is a Raring Touch image and therefore built with a
CyanogenMod kernel sans the patches you want.

I think once saucy builds are going smoothly, we can close this.

[Ricardo Salveti (rsalveti)]

They are already applied at the ubuntu kernel, and also made them available at the phablet.u.c kernel until we officially migrate to the kernel package.